1. Scope of Invention
This invention relates generally to electrical energy management systems, and more particularly to a system for interrupting the electrical power being supplied to selected electrical loads within a facility when the incoming current load exceeds a predetermined maximum level for a continuous preselected time period.
2. Prior Art
As the unit cost of electrical power being supplied into a facility increases, the incentive to control that expenditure increases as well. All facilities utilizing electric power, particularly commercial facilities, churches, schools and the like, incur peaks in the overall current consumption during time periods of minimum electrical load operation within the facility.
For example, churches and schools would have more obvious time periods of peak electrical load with respect to both lighting and air conditioning equipment when the facility is in use. Likewise, commercial restaurants encounter extreme peak electrical power usage during normal meal hours. It is during these peak load time periods that the bulk of the electrical power is consumed and thus has the greatest impact upon the overall monthly cost of electrical power.
The broad concept of limiting the maximum current consumption to a particular upper current level by various means in order to reduce electrical power consumption costs appears to be well known. The following U.S. Patents and the corresponding inventors which have addressed this challenge are set forth herebelow:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 4,090,088 McMahon, et al. 4,168,491 Phillips, et al. 4,213,058 Townsend 4,216,384 Hurley 4,336,462 Hedges, et al. 4,370,723 Huffman, et al. 4,446,359 Arribas, et al. 4,464,724 Gurr, et al. 4,471,232 Peddie, et al. 4,510,398 Culp, et. al. 4,659,943 Virant 4,694,192 Payne, et al. 4,695,738 Wilmot 4,771,185 Feron, et al. 4,808,841 Ito, et al. 4,847,781 Brown, III, et al. 5,237,207 Kwiatkowski, et al. 5,243,225 Schweer, et al. 5,278,771 Nyenya 5,281,859 Crane ______________________________________
More specifically, the Phillips' U.S. Pat. No. 4,168,491 discloses an energy demand controller and method of operation thereof, including a sensor for measuring instantaneous power being delivered to a building and a controller which allows the user to preselect a power limit for use in the building. A comparator serves to compare the input power to the preselected value and to switch off the power to various heating zones within the building in order to maintain the input power at a preselected power level. Preprioritizing determines the sequence of load interruption.
The Peddie U.S. Pat. No. 4,471,232 teaches controlling individual loads within an electrical system, a signal being transmitted over the power lines to individual loads to establish the priority sequence based upon individual load consumption.
Schweer in the U.S. Pat. No. 5,243,225 also teaches a load shedding system during peak load demand periods by transmitting a pulsed signal over each phase of a power transmission line by utilizing a phase injective transmitter and a communication link in a remote transmitter interacting upon a group of receivers.
The Brown U.S. Pat. No. 4,847,781 discloses an energy management system utilizing pulse control signals sent over the home wiring lines to control equipment utilizing on/off commands initially sent from a central control station located outside of the home.
McMahon in the U.S. Pat. No. 4,090,088 teaches the use of a control unit to continuously monitor the total power level of the facility and the sending of signals to the load control units based upon changes in this power demand level. Loads are shut off on a prioritized cycling basis, cycling being achieved on a timed basis.
In the U.S. Pat. No. 4,808,841 to Ito, peak power load control to an electric heating system is there provided. Upon detection of a preselected peak load, power is cut off to one or more heating units in succession and then reconnected. Power cut-off time is extended on a predetermined adjustable basis.
None of these references appear to disclose all of the features of the present invention in combination. More specifically, the features of utilizing a sensing unit for power input into a facility and for providing an initial interrupt signal only after the peak load exceeds a one or more preselected peak values for a predetermined continuous time period, utilizing two of the three phases of a multi-phase power transmission line for signal redundancy and reliability and the sequenced reactivating of loads on a predetermined incrementally stepped basis by the remotely located limiters are some of the features of the present invention not disclosed in these prior art references.